bloodstain pattern analysis: investigating the ... · bloodstain pattern analysis: investigating...

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BLOODSTAIN PATTERN ANALYSIS: INVESTIGATING THE

EFFECTIVENESS OF SMALL (SUB 3MM) BLOODSTAINS

IN AREA OF ORIGIN DETERMINATIONS

Brinda SALASKAR

A thesis submitted in fulfilment of the requirements for the degree of

Master of Forensic Science (Professional Practice)

in

The School of Veterinary and Life Sciences

Murdoch University

Project Supervisor: Mark Reynolds, Forensic Science Consultant, WA Police

Project Co-Supervisor: James Speers, Associate Professor in Forensic Science, Murdoch University

Semester 2, 2016

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DECLARATION

I declare that this manuscript does not contain any material submitted previously for the

award of any other degree or diploma at any university or other tertiary institution.

Furthermore, to the best of my knowledge, it does not contain any material previously

published or written by another individual, except where due references have been made

in the text. Finally, I declare that all reported experimentations performed in this research

were carried out by myself, except that any contribution by others, with whom I have

worked is explicitly acknowledged.

Signed:

Dated:

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Acknowledgements

The author would like to thank project partner Ryan Pugh for his assistance with selection

and examination of impact patterns, WA Police Forensic Consultant Dr Mark Reynolds for

his selection of large impact stains and his support and guidance on data interpretation and

Associate Prof James Speers of Murdoch University’s Forensic Science Department for his

tireless dedication and advice on this project.

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Table of Contents

Title Page ................................................................................................................................. i

Declaration.............................................................................................................................. ii

Acknowledgements ................................................................................................................ iii

Table of Contents.................................................................................................................... iv

List of Figures .......................................................................................................................... v

List of Tables.......................................................................................................................... vii

Part One

Literature Review .................................................................................................................... 1

1. Introduction.................................................................................................................. 2

2. Origins of Bloodstain Pattern Analysis............................................................................. 3

3. Current Knowledge on Bloodstain Pattern Analysis ......................................................... 5

3.1 Flight path of a Blood Droplet .......................................................................................... 5

3.1.1 Forces Acting upon a Droplet in Flight ........................................................................ 5

3.1.2 Fluid Dynamics and Dimensionless Numbers .............................................................. 6

3.1.3 Straight-line Trajectory vs. Ballistic Trajectory of Blood Droplet ................................... 8

3.2 Bloodstain Selection .......................................................................................................16

3.2.1 Shape and Form of Bloodstain ..................................................................................16

3.2.2 Impact Angle of Bloodstain.......................................................................................19

3.2.3 Size of Bloodstain.....................................................................................................22

4. Proposed Research .......................................................................................................27

5. Glossary.......................................................................................................................28

6. References ...................................................................................................................29

Part Two

Project Manuscript .................................................................................................................32

Abstract ..................................................................................................................................33

1. Introduction.................................................................................................................34

2. Materials and Methods.................................................................................................38

3. Results.........................................................................................................................42

4. Discussion ....................................................................................................................51

5. Conclusion ...................................................................................................................55

6. References ...................................................................................................................56

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List of Figures

Figure 1 Semi dimensionless plot to determine impact velocity of a falling droplet as a

function of droplet diameter (do) and initial droplet velocity (vo) for a vertical path of 1m

(Attinger et al., 2013) ............................................................................................................. 7

Figure 2 Diagrammatical representation of trigonometry associated with angle of impact

calculations. The equation is a trigonometric function of a right angle triangle. (James et al.,

2005) ...................................................................................................................................... 9

Figure 3 Diagrammatical representation of the tangent method (image by Brinda Salaskar)

............................................................................................................................................. 10

Figure 4 Visualisation of the manual string line method (image by David Spivey WA Police)

............................................................................................................................................. 11

Figure 5 Calculation of angle of impact (α) using Microsoft® Office Excel 2003 Auto Shape

program (image by Brinda Salaskar) .................................................................................... 12

Figure 6 End View of AOO determination using BackTrack Program (Carter, 2001)............ 12

Figure 7 Impact velocity vector V shown in relation to its three components, Vx, Vy, and Vz

and the virtual string. The three interlocking right triangles containing the three angles α, β

and 𝜸 are also shown (Carter, 2001).................................................................................... 13

Figure 8 The positional instant of a droplet at multiple points along its ballistic path with

straight line tangential indicators inserted (Reynolds, 2008)............................................... 14

Figure 9 Diagrammatical representation of angle of impact calculation theory. Sphere is

projected onto a surface as an elliptical stain (James et al., 2005) ...................................... 20

Figure 10 Graph showing how the error in calculating a bloodstain’s angle of impact varies

as a function of the bloodstain angle of impact itself (Pace, 2005) ..................................... 21

Figure 11 Comparison between known and calculated angles of impact (α) for bloodstains

≤3.0mm long and >3.0mm and ≤6.0mm long that have fallen onto ceramic tiles at known

impact angles. (Reynolds et al., 2009).................................................................................. 24

Figure 12 3D diagrammatical representation of AOO in relation to X, Y and Z co-ordinates

(image by Brinda Salaskar) ................................................................................................... 35

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Figure 13 Wooden apparatus and hammer used to create impact spatters (Evans, 2015)….39

Figure 14 Close up and technical photography of stain with scale using the Nikkon D5500

digital camera....................................................................................................................... 40

Figure 15 Bloodstain used in the Microsoft® Office Excel 2003 Auto Shape program with axis,

fitted ellipse and scale added (image by Brinda Salaskar) ................................................... 41

Figure 16 Large, small and actual X co-ordinate comparisons for patterns 1-10 ................. 48

Figure 17 Large, small and actual Y co-ordinate comparisons for patterns 1-10 ................. 48

Figure 18 Large, small and actual Z co-ordinate comparisons for patterns 1-10 ................. 48

Figure 19 Average displacement of large bloodstains’ calculated X, Y and Z co-ordinates from

actual values for patterns 1-10 ............................................................................................ 49

Figure 20 Average displacement of small bloodstains’ X, Y and Z co-ordinates from actual

values for patterns 1-10 ....................................................................................................... 50

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List of Tables

Table 1 Significance of the physical regimes, shown as specific regions in Fig. 1. (Attinger et

al., 2013)……………………………………………………………………………………………………………………..……7

Table 2 Increase in impact angle calculation error by the same amount of measurement error over the range of impact angles 25°-70° (Pace, 2005)……………………………………………..21

Table 3 Microsoft® Office Excel 2003 Auto Shape measurement data for large bloodstains l

>3mm and small bloodstains l < 3mm (IN BRACKETS AND BOLDED) for area of origin determinations for impact patterns 1-10…………………………………………………….…………………..44

Table 4 ANOVA statistical data for variances between small, large and actual X, Y and Z

values for impact patterns 1-10……………………………………………………………………………………….45

Table 5 Paired t-test data for variances between experimental (large and small) and actual X, Y and Z values for impact patterns 1-10………………………………………………………………………..45

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Part One

Literature Review

Investigating the Size, Shape, Formation and Ballistic

Trajectory of Bloodstains in Bloodstain Pattern

Analysis

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1. Introduction

Bloodstain pattern analysis (BPA) has been used for centuries to help in the effective

reconstruction of bloodletting events that occur at crime scenes (Attinger et al., 2013). The

International Association of Bloodstain Pattern Analysts (2007) define these events to be

as a result of, “liquid blood being acted upon by physical forces causing bloodstain and

bloodstain patterns to be deposited on various surfaces”.

The reconstruction of these events can help investigative bodies to gain a better

understanding of critical information that can assist them in the evaluation of witness

statements and crime participants’ version of events (Peschel et al., 2011). Reynolds (2008)

delves deeper into the complexities of the term ‘reconstruction’ to describe is as;

“The examination of the location, size, shape and distribution of bloodstains and bloodstain

patterns in association with knowledge of the underpinning sciences (Mathematics, Physics,

Chemistry and Biology) to provide information on an event, or sequence of events, that have

resulted in the deposition of those bloodstains or bloodstain patterns; a scientific means by

which physical, spatial and temporal components of a crime event can be inferred or

confirmed.”

Bloodstain pattern analysis and its many facets have become pivotal in determinations of

bloodletting events due to the ability of the analyst to determine the area of origin (AOO)

of each event. There are specific selection criteria when choosing bloodstains for this type

of determination which will be discussed in this literature review.

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2. Origins of Bloodstain Pattern Analysis

From its early days in 19th century Germany (Attinger et al., 2013), bloodstain pattern

analysis (BPA) has strived to understand the “how?” part of the crime puzzle. Although

informally used and researched for many years, the very first known systematic study of

bloodstains was published in 1895 by Eduard Piotrowski from the University of Krakow

titled, ‘On the formation, form, direction and spreading of bloodstains after blunt trauma

to the head’. Through his research of blunt force trauma on live rabbits Piotrowski was

able to visualise and study the patterns of bloodstains created, and postulated that the

condition for the appearance of bloodstains was the presence of an existing blood source

(Piotrowski, 1895), a finding still widely accepted to this day.

In 1954, P.L. Kirk referenced BPA in his expert testimony of a murder trial committed in

Ohio, USA (State of Ohio vs. Samuel Sheppard). Kirk showed the position of the assailant

and the victim through his reconstruction and revealed that the attacker struck the victim

with his left hand, which was significant as Sheppard was right-handed. Kirk later went on

to develop a research project based on the case and although it remains unsolved to this

day, the case marked a pivotal moment in BPA history as expert witness testimony had

never been given on the discipline before this time.

Other pioneers of BPA such as Dr. Victor Balthazard and Dr. Herbert Leon MacDonell were

the first to publish articles on angles of impact (Balthazard et al., 1939) and flight

characteristics of human blood (Macdonell, 1971) respectively. Balthazard presented an

article ‘Etude des Gouttes de Sang Projete’ to the XXII Congress of Forensic Medicine

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outlining the elements of a bloodstain that gave indications to its origin and proposed the

idea that a trigonometric sine relationship existed between the length and width of a

bloodstain ellipse. He proposed that accurate measurements of the ellipse would lead to

the determination of impact angle (α). Macdonell was the first to demonstrate

repeatability of the discipline as his work and results were remarkably similar to those done

by Balthazard. In 1973, Macdonell founded the Bloodstain Evidence Institute and

developed a basic bloodstain analysis course for law enforcement personnel. He eventually

went on to attend the first Advanced Bloodstain Institute, and along with other attendees

founded the International Association of Bloodstain Pattern Analysts (IABPA) in 1983.

In 1988 Dr. W. Eckert released a comprehensive book on the ‘Interpretation of Bloodstain

Evidence at Crime Scenes’ and five years later Dr. Chris Price and Adrian Emes were the first

to release a video, ‘Blood in slow motion’, illustrating how blood behaved under various

conditions using 4,000 frames per second recording footage.

In 2002, the Scientific Working Group on Bloodstain Pattern Analysis (SWGSTAIN) was

formed as a means to create ‘best practises’ among public and private sectors on the

disciple internationally. SWGSTAIN promoted and enhanced the development of quality

forensic BPA practices through the collaborative efforts of government forensic

laboratories, law enforcement, private industry and academia.

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3. Current Knowledge on Bloodstain Pattern Analysis

There exists a large knowledge base on BPA, ranging from its uses in crime scenes, to its

evidentiary value in court and its impact on legal proceedings. Among the array of

bloodstain patterns that can be distinguished, an impact spatter is of particular evidentiary

value and forensic interest. Impact spatter is described by the Scientific Working Group on

Bloodstain Pattern Analysis (SWGSTAIN) as , “a bloodstain pattern resulting from an object

striking liquid blood”. The radiating pattern of individual droplets that results from this can

help investigators in spatial, temporal and contextual reconstruction of the events resulting

in bloodshed. In order to use impact spatter patterns in such cases it is vital to understand

the characteristics of a blood drop and the forces acting upon its flight path.

3.1 Flight path of a Blood Droplet

3.1.1 Forces Acting upon a Droplet in Flight

Kabaliuk et al., (2014) investigated the forces acting upon fluid (blood) in motion in his work

on droplet deformation and breakup, referencing the effects of air currents and wind on

spatter drop trajectories. The study found that when a blood drop was following a ballistic

trajectory it was influenced by gravitational, inertial and aerodynamic drag forces and

depending on the mechanism of formation, the fluid drop may be non-spherical and

experience shape oscillations under the influence of surface tension (Kabaliuk et al., 2014).

These forces are the source of constant critique and research in the forensic world due to

the impact they have on AOO determinations. The article also introduced a single model

found to describe drop behaviour accurately in passive, cast off and impact scenarios. The

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model was a numerical code for accurate modelling of blood drop flight path that

incorporated gravitational and aerodynamic drag forces as well as in-flight drop

deformation, oscillations and possible secondary break-up scenarios. Although this article

included detailed description on the mechanisms of spatter drop generation and the uses

of the proposed numerical model, it did not sufficiently detail the influences and impacts

of gravitational and drag forces on a blood drop trajectory.

3.1.2 Fluid Dynamics and Dimensionless Numbers

Attinger et al., (2013) produced a more comprehensive analysis on these forces, comparing

bloodstain pattern analysis to fluid dynamics. The comparative review highlighted the

relationships between the disciplines of bloodstain pattern analysis in forensics and fluid

dynamics in the physical sciences. The article made some very valid connections between

the two disciplines and revolved around the physical forces driving the motion of blood as

a fluid; the generation of drops; their flight in the air; their impact on solid or liquid surfaces

and the production of stains. It described interactions between forensics and physics with

their joint use of dimensionless numbers, suggesting that proper use of such numbers in

the forensic field resulted in simpler analyses valid for a wider range of experimental

conditions thus allowing experimental outcomes to be inferred for cases that had not or

could not been tested explicitly. Dimensionless numbers such as the Weber number and

Reynolds number are often used in forensic science in a semi-dimensionless plot (Figure 1)

to determine the impact velocity of a falling droplet.

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The dimensionless numbers allow for the presentation of a wide range of physical regimes

in the same plot and answer fundamentally significant questions in BPA studies (Table 1).

Physical

Regime

Physical significance on the trajectory of a drop

1 Significant acceleration of droplet due to gravity forces, drag forces are significant

2 Significant acceleration of droplet due to gravity, drag forces are insignificant

3 Minor deceleration of droplet due to drag, gravity negligible with respect to drag, but gravity

significant with respect to initial kinetic energy

4 Drag forces significantly decelerate the drop; gravity negligible with respect to drag, but

gravity significant with respect to initial kinetic energy

5 High probability that drop breaks up into smaller drops during fl ight, due to shear breakup

6 Major deceleration due to drag; gravity negligible with respect to initial kinetic energy

Table 1 Significance of the physical regimes, shown as specific regions in Fig. 1. (Attinger et al., 2013)

Figure 9 Diagrammatical representation of trigonometry associated with angle of impact calculations. The

equation is a trigonometric function of a right angle triangle. (James et al., 2005) Table 2 Significance of the

physical regimes, shown as specific regions in Fig. 1. (Attinger et al., 2013)


equation is a trigonometric function of a right angle triangle. (James et al., 2005)

Figure 11 Diagrammatic representation of the tangent method (image by Brinda Salaskar)Figure 12

Diagrammatical representation of trigonometry associated with angle of impact calculations. The equation is a

trigonometric function of a right angle triangle. (James et al., 2005) Table 3 Significance of the physical

regimes, shown as specific regions in Fig. 1. (Attinger et al., 2013)


equation is a trigonometric function of a right angle triangle. (James et al., 2005) Table 4 Significance of the

physical regimes, shown as specific regions in Fig. 1. (Attinger et al., 2013)


equation is a trigonometric function of a right angle triangle. (James et al., 2005)

Figure 15 Diagrammatic representation of the tangent method (image by Brinda Salaskar)Figure 16

Diagrammatical representation of trigonometry associated with angle of impact calculations. The equation is a

Figure 1 Semi dimensionless plot to determine impact velocity of a fall ing droplet as a function of

droplet diameter (do) and initial droplet velocity (vo) for a vertical path of 1m (Attinger et al., 2013)















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Attinger et al., (2013) also mentioned one of the most debated topics in BPA: the use of

straight-line trajectories in AOO calculations. It has been discussed in many articles dating

back to those by Piotrowski (1895) and Balthazard et al., (1939) that blood follows a ‘bent’

or ‘ballistic’ trajectory and that reconstruction methods based on a straight-line trajectory

carry with it uncertainties and errors. The article goes on to briefly mention the errors

associated with these methods and the assumptions used in the calculations. Although the

article gave an exhaustive review of the two disciplines in great detail and their overlapping

interests, it did not spend enough time fulfilling the initial aim of identifying potential inter-

community collaborations or suggest the direction of future endeavours that would help

the two disciplines work most effectively together.

3.1.3 Straight-line Trajectory vs. Ballistic Trajectory of Blood Droplet

One of the most researched topics in BPA is the error associated with AOO calculation

models that assume blood droplets follow a straight-line trajectory. From its myriad of

uses, one critical function of BPA at a crime scene is its effectiveness in determining the

AOO of a bloodletting event. AOO determinations are of particular forensic interest as they

define the three dimensional location where a source of blood originated. The width and

length of a blood droplet enables determination of the impact angle by using the equation

𝐴𝑛𝑔𝑙𝑒 𝑜𝑓 𝐼𝑚𝑝𝑎𝑐𝑡 (𝛼) = 𝑎𝑟𝑐𝑠𝑖𝑛𝑒 (𝑤𝑖𝑑𝑡ℎ

𝑙𝑒𝑛𝑔𝑡ℎ) (Figure 2). Previously, the impact angle (α) and

glancing angle (𝛾) were used to compute the direction of the droplets chosen for the

determination at the instant before impact in directional analysis method introduced by

Carter (2001). These droplets were then assigned virtual strings and subsequently by

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measuring the x, y and z co-ordinates of the bloodstain, a point of origin could be estimated

at the intersection of these strings.

All current AOO determination methods are based on Euclidean geometry and straight-line

blood droplet flight path predictions. In other words, the methods are predicated on the

assumption that the path of a blood drop away from the blood source follows a straight-

line trajectory, thus eliminating the effects of gravity and drag. As such, the calculated Z

value (height of blood source) will always be higher than the actual Z value, providing an

upper blood source Z value limit. Furthermore, there is a common underestimation of

calculated impact angle (α) values due to an overestimation of ellipse length relative to

width in the initial phase of calculation. This results in a calculated X value (distance from

impact wall) being closer than the actual blood source X value (Reynolds et al., 2009) and

will be discussed further on in this review.

Figure 2 Diagrammatical representation of trigonometry associated

with angle of impact calculations. The equation is a trigonometric

function of a right angle triangle. (James et al., 2005)

Figure 74 Diagrammatic representation of the tangent method (image

by Brinda Salaskar)Figure 75 Diagrammatical representation of

trigonometry associated with angle of impact calculations. The

equation is a trigonometric function of a right angle triangl e. (James et

al., 2005)


by Brinda Salaskar)

Figure 77 Visualisation of the manual string l ine method (image by

David Spivey WA Police)Figure 78 Diagrammatic representation of the

tangent method (image by Brinda Salaskar)Figure 79 Diagrammatical

representation of trigonometry associated with angle of impact

calculations. The equation is a trigonometric function of a right angle

triangle. (James et al., 2005)


by Brinda Salaskar)Figure 81 Diagrammatical representation of

trigonometry associated with angle of impact calculations. The

equation is a trigonometric function of a right angle triangle. (James et

al., 2005)


by Brinda Salaskar)

Figure 83 Visualisation of the manual string l ine method (image by

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The three most often used methods for AOO determinations are; 1) Tangent Method, 2)

Manual Stringline Method and 3) Computer Assisted Determination. The tangent method

relies upon the trigonometric relationship of a right-angle triangle: Tan α=

opposite/adjacent. In this method, the axis of each stain is determined and a straight line

is drawn through the middle of it. The area of convergence (AOC) is then determined at

the intersection of the lines created by each of the stains. The angle of impact (I°) is

calculated using the equation I°= sin-1(width/length) and is substituted into the equation as

the “α” value. A measurement is made from the leading edge of each stain to the AOC and

is substituted into the equation as the “adjacent” value. The “opposite” value is calculated

using a rearrangement of the tangent equation and is also known as the height of the blood

source. The tangent method is diagrammatically shown in Figure 3.

Figure 3 Diagrammatic representation of the tangent method (image by Brinda Salaskar)

Figure 154 Visualisation of the manual string l ine method (image by David Spivey WA Police)Figure 155

Diagrammatic representation of the tangent method (image by Brinda Salaskar)

Figure 156 Visualisation of the manual string l ine method (image by David Spivey WA Police)

Figure 157 Calculation of angle of impact (α) using Microsoft® Office Excel 2003 Auto Shape program

(image by Brinda Salaskar)Figure 158 Visualisation of the manual string l ine method (image by David

Spivey WA Police)Figure 159 Diagrammatic representation of the tangent method (image by Brinda

Salaskar)

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The manual stringing method uses the same premise by calculating the angle of impact (α)

but then utilises a protractor to mark the second point of attachment for the stain using

strings. Each stain has a second point attached and the area at which they converge visually

is determined to be the AOC. The height and distance can then be manually distinguished

using a ruler (Figure 4).

The computer assisted method of determination use accurate stain measurements based

on the mathematical properties of an ellipse and generate virtual strings that are perfectly

shaped and located. Figure 5 shows the calculation of impact angle using the Microsoft®

Office Excel 2003 Auto Shape program and Figure 6 is the end view of an AOO

determination using the BackTrack™ program.

Figure 4 Visualisation of the manual string l ine method (image by David Spivey WA Police)


program (image by Brinda Salaskar)Figure 227 Visualisation of the manual string l ine method

(image by David Spivey WA Police)


program (image by Brinda Salaskar)

Figure 229 End View of AOO determination using BackTrack Program (Carter, 2001)Figure 230 Calculation of angle of impact (α) using Microsoft® Office Excel 2003 Auto Shape program (image

by Brinda Salaskar)Figure 231 Visualisation of the manual string l ine method (image by David Spivey

WA Police)

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Figure 5 Calculation of angle of impact (α) using Microsoft® Office Excel 2003 Auto Shape program (image by Brinda Salaskar)

Figure 6 End View of AOO determination using BackTrack Program (Carter, 2001)

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Carter (2001), was one of the first to use directional analysis to calculate the AOO of a

bloodstain. He used a model to theoretically and practically predict the AOO of a

bloodstain (Figure 7).

As shown in Figure 7 the X, Y and Z co-ordinate system assigns three planar reference co-

ordinates for area of origin determinations. The X-value relates to the parallel vertical

planar distance away from the spatter bearing surface. The Y value assigns a vertical planar

distance from a referenced point (usually a 90° wall intersection) at some point along the

spatter bearing surface and the Z value is an indication of the horizontal plane height above

a referenced horizontal surface (usually a floor) (Reynolds, 2008).

In his article, ‘The directional analysis of bloodstain patterns theory and experimental

validation’ (2001), Carter assessed two commercially available computer programs:

Figure 7 Impact velocity vector V shown in relation to its three

components, Vx, Vy, and Vz and the virtual string. The three

interlocking right triangles containing the three angles α, β and

𝜸 are also shown (Carter, 2001)

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HemoSpat© and BackTrack™. This study along with future studies confirmed previously

held views on the programs; the z co-ordinate (height) of the blood source was almost

always overestimated due to the contributions of gravity and air resistance being neglected

on drop flight path (Carter et al., 2005, Carter et al., 2006, de Bruin et al., 2011).

Furthermore, de Bruin et al., (2011) found that bloodstains located higher on the wall or

more than 50cm away from the point of origin produced the largest source of error as

gravity was a more influential factor on these flight paths.

In another study on flight path it was stated that, “due to the unknown curvatures of the

individual flight path, unknown systematic errors in the horizontal value of the location of

the blood source may occur” (Buck et al., 2011). This was in agreement with the thesis

‘Bloodstain size, shape and formation-implications for the bloodstain pattern analyst’ by

Reynolds (2008). Figure 8 demonstrates the positional instant of a droplet at multiple

points along its ballistic path with the directional components of the gravitational (blue

arrows) and air resistance (pink arrows) force vectors indicated. It also shows straight-line

tangential indicators (black lines) from the same position on the droplet as it travels along

its flight path.

Figure 8 The positional instant of a droplet at multiple points along its ballistic path with straight l ine tangential indicators inserted (Reynolds, 2008)

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Buck et al., (2011) aimed to evaluate the ballistic analyses used to approximate the

trajectories of blood drops for AOO determinations. It highlighted the main problem

associated with cases where there was a longer distance between the AOO and impact

surface; a deviation of the vertical component (height) from the expected centre of origin

due to the curved trajectory of the drop. According to the study, due to this source of error,

ballistic analysis of the bloodstain pattern in these cases was critical to confirm the

bloodstains were from the determined blood source location. The study used

photogrammetry and 3D scanning methods to document the bloodstains and then used

computer-aided design (CAD) software to compute the length of the major and minor axes

of the ellipses. It revealed that 3D documentation and the use of ballistic determination

methods enhanced the bloodstain pattern analysis reconstruction and furthermore gave

clues as to the number and position of the areas of origin, the number of blows, the

positioning of the victim and the sequences of events.

Connolly et al., (2012) on the other hand, sought out to validate the use of straight line

trajectories in their article on the effect of impact angle variations on AOO determinations.

The research article hypothesised that impact angles of between 5° and 15° would have

negligible influence on AOO estimations. Furthermore, it was hypothesised that the size of

the area of origin would affect the influence of the angle of impact variations, thus

validating the use of straight-line trajectories as a robust and reliable method. The study

concluded that the size of the area of origin determined the level of accuracy necessary in

angle of impact estimations, i.e. as the size of the true area of origin increased, larger errors

were tolerated in the estimation. Additionally, the study also showed that an impact angle

16

of ±5° could, in certain conditions, produce a significant difference between the true and

estimated areas of origin however, this required all bloodstain angles to have errors of

≥5°and an area of origin ≤14cm. It also stated that large inaccuracies may occur in some

impact angle calculations but did not result in a significant change in the area of origin

estimate. It was suggested that the utilisation of the bloodstain selection model by Illes

and Bouè (2011) was sufficient enough to enable the use of straight-line trajectories and

generate a valid and reliable estimate of point of origin (Connolly et al., 2012).

3.2 Bloodstain Selection

Due to the potential source of error regarding straight-line trajectories mentioned above,

there are specific characteristics of blood droplets sought out by BPA analysts in their AOO

determinations that help minimise or reduce these effects of error and increase accuracy.

Stain selection is the first of these factors as the stain itself must have enough ‘useable’

droplets on each side of its pattern to be suitable for determination methods. The droplets

must be well formed (elliptical, symmetrical with well-formed leading edge), between 3mm

and 8mm, fast upward travelling and in a location of ‘10 and 2’ on a clock face relative to

the bloodstain pattern. The second factor is stain measurement, which is influenced by the

analyst’s experience, attention to detail and equipment used. Both factors affect the angle

of impact and consequently the AOO determination.

3.2.1 Shape and Form of Bloodstain

Research by de Bruin et al., (2011) described the factors affecting AOO determinations and

ways in which to improve them. The article discussed three main components of AOO

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calculations: software used, bloodstain selection and external influences. In the software

component, they determined that both HemoSpat© and BackTrack™ yielded relatively

similar analysis thus concluding that both programs performed point of origin

determinations equally well. It discussed the importance of selecting blood drops that had

large surface areas and a more elliptical shape (smaller angle of impact) as they produced

less deviation from the actual point of origin and gave more reliable results. Both these

points are in agreement with previously accepted notions about stain selection. The last

variable tested in the article was in relation to number of walls. It stated that using more

than one wall for AOO determinations reduced the deviations in the X (distance from wall)

and Z (height) direction. In summary the article acknowledged and further validate already

known practises adopted by BPA analysts. Unfortunately, there were no new or novel

techniques suggested or tested in this article and although it touched on a few important

factors in stain selection, the content did not deliver any origina l “improvements to area of

origin determinations” which was an overall disappointment.

For most BPA analysts the elliptical shape of bloodstains gives the most information in

determinations of area of origin. However, an article by Kettner et al., (2015), chose to

evaluate the value of information derived from the patterns of circular bloodstains which

have been thought to hit adjacent surfaces at 90-degree angles and provide indications of

the height of the object used to exert blunt force trauma. BPA analysts often use circular

bloodstains as a quick and rough guide to estimate the height of an impact spatter however

this article indicated this may not always be the case. The study demonstrated that two

distinct patterns (clusters) of circular bloodstains were regularly found on an impact site

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after a single blow to a bleeding wound. The clusters were influenced by impact site-to-

wall distance and did not directly reflect impact height level as a rapid tool for BPA

reconstruction purposes, thus should be more used as a guide rather than a determining

factor. The most notable feature of the study was that it discussed in great depth the

formation of the two cluster stains which may in future help prevent erroneous bloodstain

pattern analysis e.g. Interpreting the presence of two stains being the result of two impacts

(Kettner et al., 2015).

An article by Adam (2012) investigated another facet of BPA: bloodstain formation. The

work aimed to examine the stains formed following an impact on paper of blood droplets

in the millimetre size range and travelling at a variety of angles and velocities. It also

reviewed the current theoretical models for spreading and splashing of liquid drops on

surfaces. During bloodstain formation at the point of impact, a lamella (boundary layer of

liquid) is created when the droplet comes in contact with a surface. This layer spreads

rapidly in a radial direction while the majority of the droplet remains spherical. This stage

is followed by the rim of the lamella swelling as liquid flows outwards from the spherical

reserve to create a largely flat, disc-like entity with a swollen rim. The material within the

rim may then recede inwards until equilibrium is attained (Adam, 2012). The preceding

stain formation has been ascribed into four phases: contact/collapse; displacement;

dispersion and retraction, with fluid dynamic reviews having demonstrated a generic

likeness in these stain formation phases regardless of fluid properties (Reynolds et al.,

2009).

19

A review of the current theoretical models in the article by Adam (2012) concluded that

there were fundamental mathematical expressions that enabled the understanding of

bloodstain characteristics according to the principles of physics and mathematics thereby

putting interpretation of bloodstain patterns on a sound theoretical basis. The study also

showed that for perpendicular impact the interpretation of a single stain may provide

information on its impact conditions, though, only within very limited ranges of velocities

would the calculations of droplet size and impact speed be achievable to a good degree of

accuracy. For non-perpendicular impact, the current models were concluded to give more

of an “approximation” thus there remains a gap in rigorous theoretical examinations of

such systems. It was proposed that predictions of droplet size and impact speed of non-

perpendicular impact may be possible with appropriate modifications to the expression for

the perpendicular model. The study highlighted limitations in calculations of impact angle

from the stain aspect ratio and also suggested future research into the effect of surface

properties on bloodstain formation.

3.2.2 Impact Angle of Bloodstain

The angle of droplet-to-surface impact, or alpha (α), can be defined as the “acute or internal

angle formed between the direction of a blood drop and the plane of the surface it strikes”

(Reynolds et al., 2009). The calculation for the angle of impact relies upon the assumption

that the blood droplet is spherical at the time of surface impact and that there must be a

uniform transfer of the blood sphere’s fluid content onto the surface to result in a

geometric ellipse shape as demonstrated in Figure 9.

20

Pace (2005) followed a similar path to the article by de Bruin et al., (2011) on reconstruction

methods but only focused on one factor affecting area of origin determinations: impact

angle. As mentioned above, BPA analysts abide by certain rules when selecting bloodstains

for reconstruction purposes. Bloodstains between 3mm and 8mm are most often selected

because they show the least deviation when using AOO calculation methods, a practice

that is validated by a number of studies (Brodbeck, 2012, de Bruin et al., 2011, Peschel et

al., 2011, Reynolds et al., 2009).

The article by Pace (2005) aimed to identify and investigate where sources of error may be

introduced in AOO determinations and reflected on the error relationship between ellipse

fitting and the increased degree of error in angle of impact calculations.

Figure 9 Diagrammatical representation of angle of impact

calculation theory. Sphere is projected onto a surface as an

ell iptical stain (James et al., 2005)






















21

It was found that as the bloodstains became more rounded, i.e. angle of impact closer to

90°, the error rate became more pronounced too (Figure 10). Also, as the impact angle

increased the more prominent 1mm errors in length measurements became (Table 2).

Figure 10 supports previously held studies by de Bruin et al., (2011) which suggest choosing

more elliptical blood droplets decreases deviation in AOO calculations. Table 2 shows the

error in the angle of impact calculation is practically negligible up to impact angle of around

50°, thereafter it increases rapidly, a 2mm difference in ellipse length (highlighted) resulted

in a 12.7° error margin. It is immediately apparent therefore, as the angle of impact

increases, even a small measurement error will make a large difference in subsequent

calculations (Pace, 2005).

Table 2 Table showing the increase in impact angle calculation error by the same amount of measurement

error over the range of impact angles 25°-70° (Pace, 2005)

Figure 279 Graph showing how the error in calculating a bloodstain’s angle of impact varies as a function of

the bloodstain angle of impact itself (Pace, 2005)Table 17 Table showing the increase in impact angle

calculation error by the same amount of measurement error over the range of impact angles 25°-70° (Pace,

2005)


the bloodstain angle of impact itself (Pace, 2005)

Figure 281 Comparison between known and calculated angles of impa ct (α) for bloodstains ≤3.0mm long

and >3.0mm and ≤6.0mm long that have fallen onto ceramic ti les at known impact angles. (Reynolds et al.,

2009)Figure 282 Graph showing how the error in calculating a bloodstain’s angle of impact varies as a

function of the bloodstain angle of impact itself (Pace, 2005)Table 18 Table showing the increase in impact

angle calculation error by the same amount of measurement error over the range of impact angles 25°-70°

(Pace, 2005)




2005)




2005)




2005)

Figure 10 Graph showing how the error in calculating a

bloodstain’s angle of impact varies as a function of the

bloodstain angle of impact itself (Pace, 2005)

22

3.2.3 Size of Bloodstain

In much of the literature relating to bloodstain pattern analysis and stain selection,

bloodstain size is probably the least researched area of the field. Bloodstain size is one of

the predominant factors influencing blood drop selection for area of origin determinations

but has been neglected in terms of research. According to the formative literature by the

likes of Balthazard et al., (1939), de Bruin et al., (2011) and Attinger et al., (2013) manual

bloodstain measurement methods related to maximising accuracy and precision have seen

a preferred selection of bloodstains for reconstruction, in part related to size. Bloodstains

selected most often for these determinations are generally proportionally larger than other

physically and geometrically suitable stains present within an impact pattern (Reynolds,

2008) due to the increased likelihood of manual measurement error as the droplets

become smaller. Although there are a range of studies proving this premise to be correct

there is no real evidence supporting the premise that larger bloodstains give more accurate

results in comparison to smaller bloodstains. With the ever developing nature of BPA and

technology such as digital photography and computer assisted ellipse fitting methods the

range of bloodstains that can be included in reconstructions has significantly increased.

This magnifies the research gap in bloodstain size selection and brings into question if larger

bloodstains really are the most accurate selection method or if smaller bloodstains can be

just as precise and accurate when used in conjunction with more novel technology.

An article by Reynolds et al., (2009) was the first of its kind to comparatively demonstrate

the use of small versus larger bloodstains in area of origin determinations using a novel

computer assisted program Microsoft® Office Excel 2003 Auto Shape and the industry

23

standard program BackTrack™ Images. The article highlighted the literature gap regarding

the role of inertial, viscous and surface tension forces during droplet impact and the

formation of a bloodstain.

Studies have shown that internal pressure of any blood droplet is inversely proportional to

radius and for very small droplets, the greatest influence on shape and consequently size,

is surface tension (Raymond et al., 1996b). Reynolds et al., (2009) stated that due to angle

of impact calculations being based on the length to width ratios of a bloodstain, any relative

changes to that ratio due to the interplay of competing forces governing droplet spread,

had the potential to influence bloodstain measurement outcomes. In order to compare

the applied measurement resolution of small bloodstains against theoretical expectations,

a two-part study was undertaken. The first part of the study analysed bloodstains caused

by droplets falling vertically (under the influence of gravity alone) onto a range of inclined

surfaces with known angles. The results showed that for small bloodstains (<3mm long)

impacting a surface at angles <20°, the calculated angles of impact did not agree with

theoretical expectations. In fact, it showed that deviation increased as the obliqueness of

the impact angle increased (Figure 11). The small bloodstains consistently showed an over-

estimation of impact angle which would be as a direct result of under-estimations of ellipse

length relative to ellipse width. Subsequently this would mean that the calculated area of

origin would be further away than the theoretical expected area of origin. Previous studies

however have only ever reported over-estimations of ellipse length and consequently

under-estimations of impact angles resulting in area of origins to be calculated as closer

24

than expected area of origin (Connolly et al., 2012, de Bruin et al., 2011, Illes and Boue,

2011).

For the second part of the study, when small bloodstains (sub 3mm) were used in AOO

determinations the results demonstrated positive X co-ordinate values for seven out of the

ten patterns (70%) i.e. an over-estimation of impact angles. Of these seven patterns, 65%

had calculated impact angles of ≤25.0°. In comparison, of the three patterns with equal or

negative X co-ordinate values only 28% of calculated impact angles were ≤25.0°. When

larger bloodstains were used for comparison purposes, results showed negative or equal X

co-ordinate values for all ten patterns. This is agreement with previous studies of larger

bloodstains that demonstrate the same result regarding under-estimation of impact angles

resulting in AOO determinations to be closer than the theoretical AOO. Of the larger

Figure 11 Comparison between known and calculated angles of impact (α) for bloodstains ≤3.0mm long and

>3.0mm and ≤6.0mm long that have fallen onto ceramic ti les at known impact angles. (Reynolds et al., 2009)

Figure 290 3D diagrammatical representation of AOO in relation to X, Y and Z co-ordinates (image by

Brinda Salaskar)Figure 291 Comparison between known and calculated angles of impact (α) for bloodstains

≤3.0mm long and >3.0mm and ≤6.0mm long that have fallen onto ceramic ti les at known impact angles.

(Reynolds et al., 2009)

Figure 292 3D diagrammatical representation of AOO in relation to X, Y and Z co-ordinates (image by Brinda Salaskar)

Figure 293 Wooden apparatus and hammer used to create impact spatters (Evans, 2015)Figure 294

3D diagrammatical representation of AOO in relation to X, Y and Z co-ordinates (image by Brinda

Salaskar)Figure 295 Comparison between known and calculated angles of impact (α) for bloodstains ≤3.0mm

long and >3.0mm and ≤6.0mm long that have fallen onto ceramic ti les at known impact angles. (Reynolds et

al., 2009)




(Reynolds et al., 2009)




25

bloodstains used in AOO calculations, 60% of calculated impact angles were ≤25° but as

expected the length and width of the ellipses were proportionately larger to the small

bloodstains used. When compared to each other the percentage of bloodstains with

calculated impact angles ≤25° between the smaller size bloodstain sample set and the

larger size set was essentially the same; 65% and 60% respectively.

Although the study was unable to pinpoint the exact cause of this apparent shift in X co-

ordinate values, it did suggest likely causes; “results suggest the variance is associated to

changes in relative influences of competing forces namely inertia, viscosity and in particular

surface tension during droplet to bloodstain transition” (Reynolds et al., 2009).

Furthermore, it stated that as blood droplet size and surface impact angle decreased, the

relative influence of surface tension on stain formation increased, which resulted in the

over-estimations of calculated impact angles.

The study concluded that until further research was conducted into identification and

quantification of the influences of the aforementioned forces on the formation and

geometric display of small blood drops they should not be used for AOO reconstruction

purposes. The study was very thorough in its experimental design and conclusions

however; it could have included more on the limitations to the study. For example, the use

of tiles modified to mimic different angles of impact and subsequently dried horizontally

did not reflect real life conditions. This method of using passive droplets only took into

consideration the effect of gravity on droplet formation and neglected drag and inertial

forces. The method of horizontally drying the tiles after droplet impact would have

26

influenced the spreading and drying of the stain to occur differently from if it was drying

vertically on a wall. Given however, that this was one of the first research papers to suitably

investigate a core bloodstain selection process it was thorough and precise in its findings.

The need for further validating research is however apparent and mentioned within the

article.

As can be seen from the aforementioned articles, there was a vast expanse of research

conducted in the BPA field. The research however, did not thoroughly reflect or sufficiently

encompass bloodstain selection or its criteria. As one of the most fundamental parts of

BPA and AOO determinations it seemed negligent that justifications and further research

into the stain selection criterion had not been adequately provided. A research gap was

evident and should be rectified with future research.

27

4. Proposed Research

The aim of my research is to further investigate the effectiveness of small (sub 3mm)

bloodstains in AOO determinations and visualise the apparent shift in influences of inertia

and surface tension on increasingly oblique impact angles. The null hypothesis is that there

will be no significant difference in the small (<3mm) bloodstains when compared to the

larger (>3mm) bloodstains. The specific objectives will be to comparatively determine if;

1. Sub 3mm bloodstains can be used as effectively as the industry accepted

standard (between 3mm and 8mm) bloodstains in AOO determination.

2. Deviation from actual AOO increases in sub 3mm droplets as the impact angles

become increasingly oblique.

To do this, all stain widths, lengths and impact angles will be generated using the Microsoft®

Office Excel 2003 Auto Shape program. Subsequently, the AOO will be determined using

the Tangent Method.

The AOO determinations for each of the ten patterns as replicates will be statistically

analysed using the Analysis of Variance (ANOVA) statistical test in MS Excel where

comparisons will be made between the small (sub 3mm) bloodstains and >3mm

bloodstains as well as with the true AOO for each pattern. Depending on the results of the

ANOVA, post-hoc tests may or may not be undertaken.

28

5. Glossary

Listed below are terms used in this literature review. Definitions have been adapted from

the SWGSTAIN Terminology Manual (2013) unless otherwise stated.

Angle of Impact

The acute angle (alpha), relative to the plane of a target, at which a blood drop strikes the target

Area of Origin

The three- dimensional location from which spatter originated

Bloodstain A deposit of blood on a surface

Bloodstain Pattern A grouping or distribution of bloodstains that indicates through regular or repetitive form, order or arrangement the manner in which the pattern was deposited

Flight path

The path of the blood drop as it moves through space from the impact site to the target (Reynolds, 2008)

Impact Pattern

A bloodstain pattern resulting from an object striking liquid blood

Passive drop A bloodstain drop created or formed by the force of gravity acting alone

Spatter Stain

A bloodstain pattern resulting from a blood drop dispersed through the air due to an external force applied to a source of liquid blood

Target

A surface onto which blood has been deposited

Terminal Velocity The maximum speed to which a free-falling drop of blood can accelerate in air which is

approximately 25ft/sec (Reynolds, 2008)

29

6. References

ADAM, C. D. 2012. Fundamental studies of bloodstain formation and characteristics.

Forensic Sci Int, 219, 76-87.

ATTINGER, D., MOORE, C., DONALDSON, A., JAFARI, A. & STONE, H. A. 2013. Fluid dynamics

topics in bloodstain pattern analysis: comparative review and research opportunities .

Forensic Sci Int, 231, 375-96.

BALTHAZARD, V., PIEDELIEVRE, R., DESOILLE, H. & DEROBERT, L. 1939. Etude des Gouttes

de Sang Projecte (Study of Projected Drops of Blood). Ann Med Leg Criminol Police Sci

Toxicol, 19, 265-323.

BRODBECK, S. 2012. Introduction to Bloodstain Pattern Analysis Journal for Police Science and Practice 2, 51-57.

BUCK, U., KNEUBUEHL, B., NATHER, S., ALBERTINI, N., SCHMIDT, L. & THALI, M. 2011. 3D

bloodstain pattern analysis: ballistic reconstruction of the trajectories of blood drops and

determination of the centres of origin of the bloodstains. Forensic Sci Int, 206, 22-8.

CARTER, A. L. 2001. The Directional Analysis of Bloodstain Patterns - Theory and

Experimental Validation Canadian Society of Forensic Science 34, 173-189.

CARTER, A. L., FORSYTHE-ERMAN, J., HAWKES, V., ILLES, M., LATURNUS, P. L., LEFEBVRE, G.,

STEWART, C. & YAMASHITA, A. B. 2006. Validation of the BacktrackTM suite of programs for

bloodstain pattern analysis. J Forensic Identification, 56, 242-245.

CARTER, A. L., ILLES, M., MALONEY, K., YAMASHITA, A. B., ALLEN, B., BROWN, B.,

DAVIDSON, L., ELLIS, G., GALLANT, J., GRADKOWSKI, A., HIGNELL, J., JORY, S., LATURNUS,

P. L., MOORE, C. C., PEMBROKE, R., RICHARD, A., SPENARD, R. & STEWART, C. 2005. Further

validation of the Backtrack computer program for bloodstain pattern analysis-precision

and accuracy. IABPA News, 3.

CONNOLLY, C., ILLES, M. & FRASER, J. 2012. Effect of impact angle variations on area of

origin determination in bloodstain pattern analysis. Forensic Sci Int, 223, 233-40.

DE BRUIN, K. G., STOEL, R. D. & LIMBORGH, J. C. 2011. Improving the point of origin determination in bloodstain pattern analysis. J Forensic Sci, 56, 1476-82.

ILLES, M. & BOUE, M. 2011. Investigation of a model for stain selection in bloodstain

pattern analysis. Canadian Society of Forensic Science, 44, 1-12.

JAMES, S., KISH, P. & SUTTON, T. P. 2005. Principles of bloodstain pattern analysis: theory

and practice Boca Raton, FL, CRC Press.

30

KABALIUK, N., JERMY, M. C., WILLIAMS, E., LABER, T. L. & TAYLOR, M. C. 2014. Experimental

validation of a numerical model for predicting the trajectory of blood drops in typical crime

scene conditions, including droplet deformation and breakup, with a study of the effect of

indoor air currents and wind on typical spatter drop trajectories. Forensic Sci Int, 245, 107-20.

KETTNER, M., SCHMIDT, A., WINDGASSEN, M., SCHMIDT, P., WAGNER, C. & RAMSTHALER,

F. 2015. Impact height and wall distance in bloodstain pattern analysis --what patterns of

round bloodstains can tell us. Int J Legal Med, 129, 133-40.

MACDONELL, H. 1971. Flight Characteristics and Stain Patterns of Human Blood. US Dept of Justice NIJ Pub, 77.

PACE, A. 2005. The relationship between errors in ellipse fitting and the increasing degree

of error in angle of impact calculations. IABPA News, 3, 12-14.

PESCHEL, O., KUNZ, S. N., ROTHSCHILD, M. A. & MUTZEL, E. 2011. Blood stain pattern analysis. Forensic Sci Med Pathol, 7, 257-70.

PIOTROWSKI, E. 1895. Ueber Entstehung, Form, Richtung und Ausbreitung der Blutspuren

nach Hiebwunden des Kopfes [On the formation, form, direction, and spreading of blood stains after blunt trauma to the head].

RAYMOND, M. A., SMITH, E. R. & LIESEGANG, J. 1996. The physical properties of blood--

forensic considerations. Sci Justice, 36, 153-60.

REYNOLDS, M. 2008. Bloodstain Size, Shape and Formation; implications for the bloodstain

pattern analyst. Masters of Forensic Science/ Doctor of Philosophy, University of Western

Australia.

REYNOLDS, M., RAYMOND, M. A. & DADOUR, I. 2009. The use of small Bloodstains in Blood

Source Area of Origin Determinations. Canadian Society of Forensic Science, 42, 133-146.

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32

Part Two

Project Manuscript

The Effectiveness of Small (sub 3mm) Bloodstains on

Area of Origin Determinations

33

Abstract

The use of bloodstain pattern analysis (BPA) in reconstruction of bloodletting events has

become a critical and integral part of many criminal investigations and court cases. In

instances where a bloodstain pattern is created due to external forces being applied to a

source of blood, an impact spatter pattern is created. Traditionally, BPA analysts have

followed a rigid protocol for selection of bloodstains used in these reconstruction events in

attempts to lessen sources of error that directly impact area of convergence (AOC) and area

of origin (AOO) calculations. One such selection criteria is bloodstain size; bloodstains that

have a length (l) between 3mm and 8mm are considered useful for reconstruction

determinations. The purpose of this study was to evaluate the effectiveness of small (l

<3mm) bloodstains in AOO determinations in comparison to the accepted industry

standard and identify the involvement of impact angles in these calculations. Bloodstain

impact angles and AOO calculations were conducted using the Microsoft® Office Excel 2003

Auto Shape program and tangent method respectively. Bloodstain size was found to have

no impact on X (p-value=0.906), Y (p-value=0.262) and Z (p-value=0.688) co-ordinates for

AOO determinations and decreasing angles of impact showed no correlation to deviation

from the actual AOO.

Keywords: droplet size, area of origin, bloodstain pattern analysis, impact angle, ellipse,

forensic science

34

1. Introduction

In Western Australia the number of violent crimes accounted for 77% of total offences

against a person from June 2015 to June 2016 (WAPOL Crime Statistics Portal).

Furthermore, according to the Australian Bureau of Statistics, in 2015 homicide rates in

WA increased by approximately 33% since the previous year and assault increased by 17%

since 2014, representing the largest recorded increase over a 12-month period in any state

or territory in Australia. Naturally with the increasing number of violent crimes, there has

also been an increasing demand for forensic specialties such as bloodstain pattern analysis

(BPA). BPA has been used for centuries in the determination of circumstances resulting in

a bloodletting event (Attinger et al., 2013). It has proved to be a critical and sometimes

pivotal piece of evidence that help the finders of fact piece together events of a violent

and at times, fatal incident.

Among the array of bloodstain patterns that can be distinguished, an impact spatter is of

particular evidentiary value and forensic interest (Peschel et al., 2011). Impact spatter is

described by the Scientific Working Group on Bloodstain Pattern Analysis (SWGSTAIN) as,

“a bloodstain pattern resulting from an object striking liquid blood”. The radiating pattern

of individual droplets that results from this can help investigators in spatial, temporal and

contextual reconstruction of the events resulting in bloodshed.

Area of Origin (AOO) determinations are of particular forensic interest as they define the

three dimensional location where a source of blood originated. The width and length of

selected stains within an impact pattern result in the determination of impact angles (α).

35

The droplets can then assist in area of convergence (AOC) determinations by lines drawn

from the major axis of selected droplets to an area where they intersect each other in a 2D

form. AOO is an extension of this method by which the AOC location along with impact

angles from selected bloodstains result in a 3D source location from where the blood

originated.

This 3D source location is denoted the co-ordinates X, Y and Z (Figure 12) where;

X represents the blood source distance from target surface (horizontal distance to

a front wall

Y represents the blood source distance from a horizontal reference point (distance

to a side wall)

Z represents the blood source height (vertical distance from AOC to floor)

AOO determinations are based on Euclidean geometry and straight line blood droplet flight

path predictions. In other words, the methods are predicated on the assumption that the

path of a blood drop away from the blood source follows a straight line trajectory, thus

Figure 12 3D diagrammatical representation of AOO in relation to X, Y and Z co-

ordinates (image by Brinda Salaskar)

36

eliminating the effects of gravity and drag. The accuracy of AOO determination relies upon

the analyst implementing a strategic sampling rationale based on the spatial and geometric

characteristics of the spattered bloodstains present within the impact pattern (Reynolds,

2008). Consequently, there are specific characteristics of blood droplets sought out by BPA

analysts in their AOO determinations that help minimise or reduce these effects of error

and increase accuracy. One such selection criteria is blood droplet size; blood droplets with

lengths (l) of between 3mm and 8mm are considered useful in determination methods .

Other selection criteria include multiple bloodstain selection from both sides of an impact

pattern, shape (well-formed elliptical stains) and location in relation to the spatter bearing

surface (fast upward travelling droplets that lie between the ’10 and 2’ location on a clock

face)(Carter et al., 2005, James et al., 2005, Carter et al., 2006, Bevel and Gardner, 2008,

Wonder and Yezzo, 2015). Whilst experimentally these criteria can be controlled, in the

real world crime scenes don’t always follow these “perfect conditions” and other scenarios

are constantly presented and tested. Smaller blood droplets (l <3mm) are being

considered with the ever growing power of digital photography and advancements in

measurement and reconstruction software (Reynolds et al., 2009, Reynolds, 2008).

There are substantial amounts of information regarding straight-line trajectories of blood

droplets in flight (Macdonell, 1971), droplet deformation (Kabaliuk et al., 2014) and impact

angle influences on reconstruction (Adam, 2012) but minimal research regarding the

selection criteria for AOO reconstruction i.e. blood drop size and its effects on AOO

determinations. A paper by de Bruin et al., (2011) briefly mentioned the influence of

droplet size in their research into improving point of origin determinations and a thesis by

37

Evans (2015) investigated the effects of haematocrit values of blood on AOO

determinations. But it appears that within all the available research regarding AOO

determinations there is a research gap in the factors influencing droplet selection, namely

droplet size. The most recent if not only paper that discussed the influence of droplet size

in AOO determinations arose in 2009 by Reynolds et al., where a focal research point was

using small bloodstains for AOO determinations using the existing industry standard

computer assisted method BackTrack™ Images and a novel program Microsoft® Office

Excel 2003 Auto Shape. The research concluded that the use of digital photography and

computer assisted methods had broadened the range of bloodstain sizes that were able to

be used in determinations however, reflected that previously accepted notions that

bloodstains with a larger surface area corresponded to less deviation still held true. The

paper also mentioned that extrinsic and intrinsic forces affected the AOO calculations for

small (l <3mm) bloodstains that impacted surfaces obliquely at low impact angles (α<15°)

resulting in a positive direction of difference between the calculated X value and actual

blood source X value. This was opposed to the commonly calculated negative blood source

X value determinations. The hypothesised reason for this was that surface tension, inertia

and viscosity were a greater influence on the smaller droplets as they transitioned from

droplets in flight to bloodstains on an impact surface.

The ensuing study follows the research conducted by Reynolds et al., (2009) and aimed to

investigate the effectiveness of small (l <3mm) blood droplets in AOO determinations ,

where the null hypothesis showed no statistically significant differences between

determination of AOO for bloodstains <3mm in length and the accepted method (3mm to

38

8mm) for X, Y and Z values. Furthermore, it aimed to evaluate an observation put forward

in the article by Reynolds et al., (2009) where there was an overestimation of X co-ordinate

values in small bloodstains with impact angles of <15°. The null hypothesis showed no

statistically significant difference between X co-ordinate values for small bloodstains with

angles of impact <15° and actual X co-ordinate values.

For comparative purposes large blood droplets (l >3mm) were also selected and impact

spatter patterns were created by a method of blind trials. The X, Y and Z co-ordinates were

unknown to the author until all statistical and computational analyses had been completed.

Deviation from actual AOO in sub 3mm droplets as impact angles became increasingly

oblique was also briefly explored.

2. Materials and Methods

Pattern Creation

Bloodstain patterns were created using fresh (<5hrs old) whole human blood stored in

EDTA anti-coagulant tubes. Ten impact patterns were created in BPA demountable rooms

at Murdoch University by striking the head of a claw hammer onto a pool of blood (~5mL)

placed on wooden block apparatuses of varying heights (40cm and 65cm) (Figure 13). The

impact spatters were deposited onto 104cm x 156cm semi-gloss (880GSM) screen boards

affixed to the wall using all-purpose masking tape.

A BPA analyst from the Western Australian Police Forensic team generated the patterns

using consistent methodology for all ten patterns and recorded the X, Y and Z co-ordinates

for each source location. Each source location was varied in dimensions and produced by

39

a process of ‘blind trials’ so as to ensure no investigator bias was encountered. This

approach ensured all analyses conducted in this experiment relied solely on the stain

selection and calculated dimensions from the impact patterns created.

Stain Selection and Photography

Once the ten impact patterns were created and allowed sufficient time for drying

(~15mins), the BPA expert made a selection of ten droplets from each pattern that were

consistent with the selection criterion used by BPA analysts in WA Police. Selection

included well-formed fast upward travelling droplets that were appropriately distributed,

symmetrical, elliptical and between 3mm-8mm in length. Two study analysts (including the

author) then selected ten droplets with identical selection criteria bar the length of the

droplets which were limited to below 3mm. A scale and reference number was then added

next to each stain and photographed using a Nikkon D5500 digital camera with an AF-S

Micro Nikkor 60mm lens. The micro lens aperture was calibrated at f/4.0 with an ISO of 800

and shutter speed of 1/250 seconds. Figure 14 shows the types of technical photographs

taken of each stain in this study.

Figure 13 Wooden apparatus and hammer used to

create impact spatters (Evans, 2015)

Figure 308 Close up and technical photography

of stain with scale using the Nikkon D5500

digital cameraFigure 309 Wooden apparatus

and hammer used to create impact spatters (Evans, 2015)


of stain with scale using the Nikkon D5500 digital camera

Figure 311 Bloodstain used in the Microsoft®

Office Excel 2003 Auto Shape program with axis,

fitted ellipse and scale added (image by Brinda

Salaskar)Figure 312 Close up and technical

photography of stain with scale using the

Nikkon D5500 digital cameraFigure 313

Wooden apparatus and hammer used to create

impact spatters (Evans, 2015)



digital cameraFigure 315 Wooden apparatus

and hammer used to create impact spatters (Evans, 2015)



digital camera

40

Data Analyses

Each stain was subsequently analysed using the Microsoft® Office Excel 2003 Auto Shape

program to determine its impact angle (α) using the equation:

Impact angle (α)= sin-1 ( 𝑤𝑖𝑑𝑡ℎ𝑙𝑒𝑛𝑔𝑡ℎ

) [1]

The Microsoft® Office Excel 2003 Auto Shape program was chosen because it had the

capability to calculate impact angles to sub-degree levels and the ability to symmetrically

auto-elongate the measuring ellipse during the fitting process, ensuring both halves of the

ellipse were mirrored. This retained the integrity of the ellipsoid’s mathematical properties

(Reynolds, 2008) and made the program unique among its predecessors Backtrack™ and

Hemospat® for its ability to calculate ellipses to sub degree levels (de Bruin et al., 2011,

Reynolds, 2008). Macro functions such as the scaling bars were another important function

of the program as they accounted for distortion error associated with photography of the

bloodstain. Figure 15 shows the fitting process of a bloodstain used in this study using the

Microsoft® Office Excel 2003 Auto Shape program.

Figure 14 Close up and technical photography of stain with scale using the Nikkon D5500 digital camera


fitted ellipse and scale added (image by Brinda Salaskar)Figure 334 Close up and technical photography of stain with scale using the Nikkon D5500 digital camera

Figure 335 Bloodstain used in the Microsoft® Office Excel 2003 Auto Shape program with axis, fitted ellipse and scale added (image by Brinda Salaskar)

Figure 18 Large, small and actual Z co-ordinate comparisons for patterns 1-10Figure 336

Bloodstain used in the Microsoft® Office Excel 2003 Auto Shape program with axis, fitted ellipse

and scale added (image by Brinda Salaskar)Figure 337 Close up and technical photography of stain with scale using the Nikkon D5500 digital camera


fitted ellipse and scale added (image by Brinda Salaskar)Figure 339 Close up and technical

photography of stain with scale using the Nikkon D5500 digital camera


Figure 18 Large, small and actual Z co-ordinate comparisons for patterns 1-10Figure 341

Bloodstain used in the Microsoft® Office Excel 2003 Auto Shape program with axis, fitted ellipse

and scale added (image by Brinda Salaskar)Figure 342 Close up and technical photography of stain with scale using the Nikkon D5500 digital camera


fitted ellipse and scale added (image by Brinda Salaskar)Figure 344 Close up and technical

photography of stain with scale using the Nikkon D5500 digital camera


41

After photography, the blood droplets were grouped into small and large stains and using

different colours, a directional line was drawn through the long axis of each selected blood

droplet to an area where it reached its maximum length (in this case, to the bottom of the

screen board). Where the lines of each of the stains intersected on another was

determined to be the point of convergence for that group (small or large) on the pattern.

The point of convergence to the floor was determined to be the height for each pattern (Z

co-ordinate) and the point of convergence to the side wall was determined to be the Y co-

ordinate.

The Tangent method calculated the distance from the pattern bearing surface (X co-

ordinate) for each pattern first using the ten small blood droplets (l <3mm) and

subsequently the ten larger blood droplets (l >3mm) with the equation:

Tan (α)= 𝑜𝑝𝑝𝑜𝑠𝑖𝑡𝑒

𝑎𝑑𝑗𝑎𝑐𝑒𝑛𝑡 [2]


fitted ell ipse and scale added (image by Brinda Salaskar)

Figure 18 Large, small and actual Z co-ordinate comparisons for patterns 1-10Figure

350 Bloodstain used in the Microsoft® Office Excel 2003 Auto Shape program with axis, fitted ellipse and scale added (image by Brinda Salaskar)

42

These values were then averaged to determine the final X co-ordinate values for the small

and large bloodstain groups.

The known X, Y and Z co-ordinates were subtracted from the experimental results in order

to derive the directionality of difference ie. positive or negative, and subsequently the

analysis of variance (ANOVA) statistical test on Microsoft Excel was used to calculate the

variance among the AOO for each pattern, namely the experimental small (S), experimental

large (L) and the known X, Y and Z co-ordinates. The data was critically assessed at a

significance level of 0.05 and the mean, standard deviation and absolute values for the

variables (X, Y and Z co-ordinates) were also recorded. Post-hoc paired t-tests were used

as a secondary measure of comparison for each variable to determine if there were any

significantly reportable variances among the small, large and known results.

3. Results

Statistical analysis of ten sets of generated BPA bloodletting events was undertaken

between and within each impact spatter pattern group. The data is presented in terms of

average differences between experimental and known results due to the differing X, Y and

Z co-ordinates for each pattern. For each co-ordinate, an average mean, standard

deviation and absolute value were calculated for comparative purposes (Table 3) and the

calculated values vs actual values are presented in Figures 16-18. Small bloodstain size

ranged from 0.61mm-1.81mm in width and 1.42mm-2.98mm in length and large bloodstain

size ranged from 1.12mm-6.53mm in width and 3.12mm-8.36mm in length across the ten

patterns. Impact angles ranged from 17.3°-66.1°. The experimental X, Y and Z means

43

represented the displacement from the known co-ordinates (X, Y and Z) and were

presented negative or positive values (Figures 19 and 20). Negative values signify an

underestimation of the experimental co-ordinate compared to the known value and

positive values represent an overestimation (Reynolds et al., 2009). Standard deviation

represents the spread or dispersion of the groups and absolute values represent the

average displacement of the group as a whole irrespective of direction of difference

(positive or negative).

44

Table 3 Shows Microsoft® Office Excel 2003 Auto Shape measurement data for large bloodstains l

>3mm and small bloodstains l < 3mm (IN BRACKETS AND BOLDED) for area of origin determinations

for impact patterns 1-10.

Pattern Stains (n) Co-ordinates

Known Value (cm)

Experimental Value (cm) Difference (cm)

1 10 X 34 37.8 (32.7) 3.8 (-1.3)

Y 146 144.9 (145.0) -1.1 (1.0)

Z 65 66.6 (67.5) 1.6 (2.5)

2 10 X 69 61.9 (63.8) -7.1 (-5.2)

Y 139 140.6 (140.6) 1.6 (1.6)

Z 65 77.2 (80.0) 12.2 (15.0)

3 10 X 46 42.6 (44.8) -3.4 (-1.2)

Y 130 131.6 (132) 1.6 (2.0)

Z 40 43.5 (44.5) 3.5 (4.5)

4 10 X 49 47.2 (48.4) -1.8 (-0.6)

Y 181 180.2 (179.5) -0.8 (-1.5)

Z 65 68.4 (68.5) 3.4 (3.5)

5 10 X 78 80.6 (75.6) 2.6 (-2.2)

Y 152 154.5 (153.3) 2.5 (1.3)

Z 65 66.8 (67.5) 1.8 (2.5)

6 10 X 72 75.0 (76.5) 3.0 (4.5)

Y 112 124.3 (125.0) 12.3 (13.0)

Z 40 55.3 (52.4) 15.3 (12.4)

7 10 X 38 37.7 (42.0) -0.3 (4.0)

Y 121 117.5 (117.5) -3.5 (-3.5)

Z 40 40.0 (36.1) 0.0 (-3.9)

8 10 X 52 51.8 (52.9) -0.2 (0.9)

Y 119 119.4 (119.1) 0.4 (0.1)

Z 65 67.0 (66.2) 2.0 (1.2)

9 10 X 63 61.2 (61.5) -1.8 (-1.5)

Y 130 129.9 (134.2) -0.1 (4.2)

Z 40 53.7 (55.0) 13.7 (15.0)

10 10 X 40 42.0 (40.6) 2.0 (0.6)

Y 108 107.1 (110.5) -0.9 (2.5)

Z 40 47.0 (50.9) 7.0 (10.9)

Mean X -0.32 (-0.21) Y 1.20 (1.87)

Z 6.05 (6.36) Standard Deviation X 3.37 (3.84)

Y 4.26 (4.49) Z 5.65 (6.50)

Absolute Value X 2.60 (2.81)

Y 2.66 (3.13) Z 6.05 (7.14)

45

Table 4 ANOVA statistical data for variances between small, large and actual X, Y and Z values for impact patterns 1-10

F-value Degrees of freedom P-value

X co-ordinate 0.015 1 0.906

Y co-ordinate 1.431 1 0.262

Z co-ordinate 0.172 1 0.688

Table 5 Paired t-test data for variances between experimental (large and small) and actual X, Y and Z values for impact patterns 1-10

X co-ordinate Large v Actual Small v Actual Large v Small

P-value 0.769 0.825 0.906 Deg. of freedom 9 9 9

T-stat -0.303 -0.227 0.121 Y co-ordinate

P-value 0.396 0.221 0.262 Deg. of freedom 9 9 9

T-stat -0.891 -1.316 -1.196

Z co-ordinate P-value 0.008 0.013 0.688

Deg. of freedom 9 9 9 T-stat -3.387 -3.096 -0.414

Upon completion of the tangent method analyses, the following absolute displacement

from actual values for large stains were obtained: X (large)= 2.60cm ±0.63cm, Y (large)=

2.66cm ±1.26, Z (large)=6.05cm ±1.79cm. From these large bloodstains, further analyses

showed that the experimental X co-ordinate displacement from the known X value was

approximately 5% and was underestimated on average by about 0.32cm across all ten

patterns. The experimental Y co-ordinate showed a displacement from the known Y value

by about 2% and a 1.2cm overestimation across all ten patterns. The Z co-ordinate showed

the most difference in experimental versus known results, its displacement was

46

approximately 13% from the known value and was overestimated on average by about

6.05cm.

The same method of analyses was applied to the small bloodstains from the ten impact

patterns and the following absolute X, Y and Z displacement values were obtained: X

(small)= 2.19cm ±0.55cm, Y (small)= 3.13cm ±1.30cm, Z (small)= 7.14cm ±1.75cm. Further

analyses showed there to be an X co-ordinate displacement of approximately 4% and a

0.21cm underestimation on average among the ten patterns. The Y co-ordinate showed a

3% displacement of experimental results when compared to the known values and an

overestimation of 1.87cm on average. The experimental Z value showed a proportionately

larger displacement of 15% from the known results and was overestimated by

approximately 6.36cm across the ten patterns.

ANOVA was subsequently carried out on the X, Y and Z co-ordinates with a statistical

significance value of 0.05. The ANOVA statistical test results presented in Table 4

demonstrate the analysis of variance among the given co-ordinate’s calculated large,

calculated small and actual bloodstain values. The X co-ordinate showed no significant

differences among the tested variables with a p-value=0.906, as did the Y co-ordinate with

a p-value=0.262 and the Z-co-ordinate with a p-value=0.688.

Further analysis was conducted using two tailed paired t-tests for each of the co-ordinates.

A paired t-test was used due to the systemic relationships that exist between the small,

large and actual bloodstain values and was two tailed because there was a possibility a

statistically significant relationship existed in either direction. For the Z co-ordinate a one

47

tailed t-test was also carried out due to the assumptions of height always being

overestimated in AOO determinations (Buck et al., 2011). The paired t-tests results for

each co-ordinate were calculated using a significance level of 0.05 and compared actual

values against each experimental value (small and large) and experimental values against

each other. The paired t-test results are presented in Table 5. Only two of the nine paired

t-tests rejected the null hypothesis to conclude a statistically significant difference in

means; the Z co-ordinate ‘Large v Actual’ and Z co-ordinate ‘Small v Actual’ with p-values

of 0.008 and 0.013 for the two tailed t-test and 0.004 and 0.006 for the one tailed paired t-

test respectively.

There were no small bloodstains which generated impact angles of <15° in this study thus

small bloodstains with impact angles of <25° were analysed. Four bloodstains were found

to meet this criterion and originated from patterns one and ten. Pattern one had stain five,

six and nine with impact angles of 21.6°, 24.8°and 23.7° respectively. Pattern ten had stain

ten with an impact angle of 24.6°. Of these impact angles, two underestimated the X co-

ordinate value (pattern one: stain five and six) and two overestimated it (pattern one: stain

nine and pattern ten: stain ten). It was decided the dataset for small bloodstains with

impact angles <25° was not large enough for any further statistical analysis or evaluation.

48

Figure 18 Large, small and actual Z co-ordinate comparisons for patterns 1-10

Figure 17 Large, small and actual Y co-ordinate comparisons for patterns 1-10

Figure 16 Large, small and actual X co-ordinate comparisons for patterns 1-10

49

Figure 19 Average displacement of large bloodstains’ calculated X, Y and Z co-ordinates from actual values for patterns 1-10

50

Figure 20 Average displacement of small bloodstains’ X, Y and Z co-ordinates from

actual values for patterns 1-10

51

4. Discussion

A research gap in the selection criteria used by BPA personnel in the reconstruction of

bloodletting events has been identified in the course of reviewing the available BPA

literature (Reynolds et al., 2009). Bloodstain size, shape and location are all critical pieces

of the AOO puzzle; one without the other would result in the portrayal of only a snippet of

the final picture. Historically, the acceptable size range for a bloodstain used in AOO

determinations has been limited to be between 3mm-8mm in length (Illes and Boue, 2011,

de Bruin et al., 2011). This originated from the article by Raymond et al., (1996) where size

of blood droplets and their associated oscillation decay rates were investigated. The

research found that droplets that impacted a vertical surface before oscillation had

completed resulted in stains that predicted incorrect positioning of the droplet projection

point (AOO). The study suggested using droplets of a distance >1m from AOO which was

associated with larger droplets in the experiment. The study did not however investigate

whether small droplets should not be used at these distances. Recently, the advancements

made in digital photography and measurement software have allowed BPA experts to

question the “usefulness” of smaller sized bloodstains (l <3mm) as they may potentially be

an overall better fit in regards to their shape and location on a particular spatter bearing

surface encountered at a crime scene.

The ANOVA variance test used in this experiment found that there was no statistically

significant difference between experimental (small and large stains) and actual values for

the X (p-value=0.906), Y (p-value=0.262) and Z (p-value=0.688) co-ordinates. Furthermore,

52

paired t-tests found that no statistically significant difference existed between use of small

bloodstains (l <3mm) or large bloodstains (l >3mm) in determination of the experimental

X (p-value=0.906), Y (p-value=0.262) and Z (p-value=0.688) values.

de Bruin et al., (2011) found that bloodstains with larger surface areas corresponded to less

deviation in AOO determinations and it was suggested that a bloodstain width> 1.5mm

gave a greater correlation to actual AOO values; small bloodstain widths in this study

ranged from 0.61mm-1.81mm and did not show specific deviation from AOO at widths of

<1.5mm. A proposed reason for bloodstains with smaller surface areas having less accurate

results was ‘issues distinguishing edges of the bloodstains, leading to errors in width and

length measurements and subsequently impact angle errors’ (de Bruin et al., 2011). In this

study the calculated average X co-ordinate values (small and large stains) showed minimal

displacement from actual X values, however, the smaller bloodstains did show an overall

smaller displacement (-0.21cm) to the larger stains (-0.32cm). Statistically- according to

ANOVA (Table 4) and a paired t-test (Table 5)- there was no significant difference between

the small and large stains when compared to the true X co-ordinate value. The experiment

was however in agreement with research indicating X values were primarily

underestimated in AOO determinations be it the small or large stains in this study ie. closer

to the spatter bearing surface (Adam, 2012, Connolly et al., 2012, Kettner et al., 2015).

Interestingly, Reynolds et al., (2009) stated small droplets (l >3mm) with impact angles

<15° showed an increase in deviation from the actual AOO and an overestimation of X

values in these particular stains. In this experiment there were no impact angles <15° so

direct comparisons could not be drawn, however, bloodstains with impact angles <25°

53

were examined. Only four small droplets had an impact angle <25° and of these, two

overestimated the X co-ordinate value and two underestimated it. Although the dataset

was not large enough to draw definitive conclusions, the results did indicate more research

on impact angles and small bloodstains was needed. In future, for the purpose of creating

stains with smaller impact angles, the point of origin can be moved closer to the spatter

bearing surface. However, droplet oscillation is a significant factor in these cases (especially

large stains) as droplets that have not reached maximum oscillation decay may create

stains with unpredictable shapes leading to incorrect AOO determinations (Raymond et al.,

1996a).

The experimental Y co-ordinate displacement from actual AOO values for both the large

and small bloodstains was only 2% and 3% respectively. Large bloodstains fared slightly

better than the small droplets by a mere margin of 1%. Experimental Z values on the other

hand showed the most displacement among the three co-ordinates but this was an

expected result as tangent method calculations are based on an assumed straight-line

blood droplet flight path where gravity is neglected and the parabolic arc of a blood droplet

trajectory is disregarded resulting in an overestimation of height (Macdonell, 1971). The

large and small droplets showed an overall 13% and 15% displacement from the actual Z

value respectively. Both the large and small bloodstains showed no statistically significant

difference to the actual Z value (p-value (large)=0.008, p-value(small)=0.013) but small

bloodstains did show less of a statistically significant difference to actual Z values than large

bloodstains. The difference between small and large bloodstains was again negligible and

not statistically significant (p-value=0.688). This is an interesting outcome since, if there

54

was no statistically significant difference between large and small stains you would also

expect there to be negligible difference in the interplaying forces that led to the formation

of each of these stains. Surface tension for example, plays a greater role as droplet size

decreases (Reynolds et al., 2009, Attinger et al., 2013) but this was not reflected in this

study.

Pace (2005) presented a similar argument to the paper by de Bruin et al., (2011), stating

that choosing more elliptical blood droplets decreased the deviation in AOO calculations

and formed the conclusion that for impact angles above 50° even a small measurement

error made a large difference in subsequent calculations. Both articles used computer

assisted methods to determine the AOO but manual methods for ellipse measurements.

The dataset for impact angles was not controlled in this experiment and only 8 out of 200

impact angles were above 50°, seven came from pattern nine’s large stains and one from

pattern two’s large stains. It was noted that 90% of pattern nine’s stains with impact angles

>50° also measured <50cm from leading edge of the bloodstain to the AOC. Of the droplets

that had an impact angle <50° (3 out of 10 stains) 100% measured >100cm from leading

edge of the bloodstain to the AOC. This is in agreement with papers by Raymond., (1995)

and de Bruin et al., (2011) which both state a distance of >1m improves AOO

determinations.

It was also interesting to note that those patterns with large displacements for X, Y and Z

followed the same trend whether they were small or large stains (patterns 2, 6, 9 and 10

shown in Figures 19 and 20). This highlights that stain selection plays a huge role in

subsequent analyses and demonstrates real world conditions in that not all spatter

55

patterns encountered at a crime scene have perfect or optimal stains available for

selection.

5. Conclusion

In recent years, technological advances have far superseded the forensic science and legal

fields and more times than not scientific procedures and forensic practices are being

questioned by the judicial system and intelligence agencies. In BPA, small bloodstains have

not been considered “useful” in AOO determinations because of their supposed

unpredictable behaviour and the unknown nature of the forces that act upon them. This

study has demonstrated that small bloodstains (l <3mm) can be employed in AOO

determinations when used in conjunction with computer assisted ellipse fitting programs

such as Microsoft® Office Excel 2003 Auto Shape and digital photography. No statistically

significant difference between the small bloodstains (l <3mm) and large bloodstains

(3mm> l <8mm) was reported in the analysis of this data and small bloodstains did not

consistently show overestimation in X co-ordinate values at impact angles of <25° as

observed by Reynolds et al., (2009). This paper, along with the study by Reynolds et al.,

(2009) has highlighted the minimal research conducted in bloodstain selection criteria for

AOO determinations and the research presented here is only one step in the right direction.

Future investigation into smaller bloodstains in AOO determinations and effects of impact

angles on X co-ordinate calculations must be conducted to give more weighting to the

preliminary findings of this study as the research here is compelling but not exhaustive.

56

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